主要区别就是look at为动词+介词短语，而take a look at是动词+名词+介词短语，两者意思都可表示看看，具体的不同如下

look at中文意思是v. 看；考虑；着眼于

Look at the time! We'll be late.看几点了！我们要迟到了。

take a look at中文意思是看一看；检查

I had to get out of the rat race and take a look at the real world again.我必须退出这种你争我夺的生活，重新看看真实的世界。